Effect of rare earths on selective hydrogenation of p-chloronitrobenzene over PtMOx/CNTs catalysts

The effect of rare earths （Sm, Pr, Ce, Nd and La） on the hydrogenation properties ofp-chloronitrobenzene （CNB） over Pt/CNTs catalyst was studied in ethanol at 303 K and normal pressure. The results exhibited that the hydrogenation of p-CNB could be carried out over PtMOx/CNTs catalysts. Both catalytic activities and yields ofp-chloroaniline （CAN） were all improved. PtCeOx/ CNTs catalyst exhibited the best catalytic activity （TOF was 0.47 s^-1） and the highest yield of p-CAN （97.5 mol%）. PtCeOx/CNTs （1.0 wt%） catalyst exhibited good stability on the hydrogenation of p-CNB.

A Highly Efficient and Selective Water-Soluble Bimetallic Catalyst for Hydrogenation of Chloronitrobenzene to Chloroaniline

Selective hydrogenation of chloronitrobenzene(CNB) to chloroaniline(CAN) catalyzed by water-soluble Ru/Pt bimetallic catalyst in an aqueous-organic biphasic system was studied. It was found that the catalytic activity increased obviously due to the addition of platinum. Ru/Pt bimetallic catalysts exhibited a strong synergistic effect when the molar ratio of Pt was in the range of 5%—80%. Under the mild conditions including a temperature of 25 ℃, a hydrogen pressure of 1.0 MPa and a Pt molar ratio of 20%, the conversion of p-chloronitrobenzene(p-CNB) reached 99.9%, with the selectivity to p-chloroaniline(p-CAN) equating to 99.4%. The Ru/Pt catalyst also showed high activity and selectivity for the hydrogenation of other chloro- and dichloro-nitrobenzenes with different substituted positions. In addition, the catalyst can be recycled five times without significant loss of activity.

Liquid Phase Hydrogenation of <i>p</i>-Chloronitrobenzene on Au-Pd/TiO₂Catalysts: Effects of Reduction Methods

The effects of palladium addition and the reduction methods on Au/TiO2 were investigated. Pd was loaded on TiO2 firstly by incipient-wetness impregnation, Au was then loaded by deposition-precipitation method. The nominal loadings of Au and Pd were 1 wt% and 0.01 wt%. The bimetallic catalysts were reduced by heating at 453 K, by flowing H2 at 423 K, or by NaBH4 at 298 K. The catalysts were characterized by ICP, XRD, TEM, HRTEM, TPR and XPS. Hydrogenation of p-chloronitrobenzene was carried out at 1.2 MPa H2 pressure and 353 K. The results showed that even adding very small amount of Pd could enhance activity and selectivity of p-chloroaniline significantly. Pd and Au formed alloy and Pd could donate partial electron to Au. Pd metal on the surface of alloy could adsorb hydrogen and enhanced the activity. The pretreatment methods did not change particle size significantly, all were below 4 nm. The sample reduced by NaBH4 could have higher concentration of Au0 and sustain small Au particle size, resulting in high activity.

Methoxylation and Direct Hydrogenative Coupling of Chloronitrobenzenes in Continuous Flow

A novel continuous flow method for the methoxylation of chloronitrobenzenes was developed. The reaction went smoothly and high yields were achieved under the optimized conditions. Furthermore, up to 76% yield of azoxybenzenes were obtained from the corresponding nitrobenzenes in the presence of NaOH in continuous flow. Compared to batch conditions, the reaction time was significantly shortened, and the chemical waste was reduced obviously.